The present invention generally relates to the field of reciprocating saws.
Reciprocating drive mechanisms are known in the art. See, for example, U.S. Pat. No. 5,050,307, issued to Palm on Sep. 24, 1991, U.S. Pat. No. 5,025,562, issued to Palm on Jun. 25, 1991, and U.S. Pat. No. 5,079,844, issued to Palm on Jan. 14, 1992, each of which is assigned to the assignee of the present invention, and is incorporated herein by reference.
Reciprocating drive mechanisms are found, for example, in reciprocating saws. Such reciprocating saws typically include a housing including a gear case, a motor in the housing having a motor shaft, a jackshaft mounted in the housing parallel to the motor shaft, and a gear and pinion connecting the motor shaft to the jackshaft. A primary wobble plate, including a drive arm, is mounted on the Jackshaft, and a tubular spindle is mounted in the gear case for reciprocating motion. The spindle has a longitudinal slot, and the drive arm projects through the slot where it is connected to the portion of the spindle opposite the slot on the other side of the axis of the spindle. The drive arm reciprocates the spindle as the jackshaft is rotated. A secondary wobble plate is mounted on the Jackshaft, and includes a drive arm for reciprocating a counterbalance that is coaxial with the spindle, to reduce vibration.
Some hand held electric tools, such as electric screwdrivers, include clutch mechanisms that activate at a torque less than the stalling torque of the motor in the tool. For example, when a screw driven by an electric screwdriver has been driven all the way into a wall, the clutch will activate to prevent stripping of the threads. Because the clutch activates at a torque less than the stalling torque of the motor, the motor in the tool continues to rotate after the clutch has activated.
Attention is directed to U.S. patent application Ser. No. 08/275,151, filed Jul. 14, 1994, now U.S. Pat. No. 5,588,496, which is assigned to the assignee of the present invention, and which is incorporated herein by reference.
The inventor of the present invention has recognized that in a reciprocating saw, the saw bit occasionally locks or binds, for example if a blade encounters a knot in wood being sawed, or is otherwise overloaded. Also, the spindle of a saw occasionally hits a work piece. Either situation creates a high energy impulse of short duration on the drive mechanism of the saw. Such an impulse can cause failure to occur in the saw. For example, wobble plates may bend, or bearings may be damaged. Such an impulse can cause failure to occur at the gear and pinion. This is the most serious type of failure, as these parts are expensive to replace.
The invention provides a reciprocating saw comprising a housing, a spindle mounted for reciprocating motion within the housing, a gear rotatably mounted within the housing, a wobble shaft rotatably mounted within the housing, a wobble plate rotatably mounted on the wobble shaft and connected to the spindle, and a clutch drivingly connecting the gear to the wobble shaft. In accordance with one aspect of the present invention, the clutch includes a clutch driver rotatably positioned within the housing adjacent the wobble shaft, and the clutch driver includes a recess for insertably receiving a portion of the wobble shaft. By virtue of the recess, the transfer of power from the clutch driver to the wobble shaft occurs through a larger surface area, thereby reducing the likelihood of failure.
Preferably, the saw further comprises a shaft rotatably mounted within the housing, and the clutch driver and the wobble shaft are positioned about the shaft. For example, the clutch driver can include an orifice for receiving the shaft, and the recess can extend substantially completely around the orifice. The clutch driver and the wobble shaft are mounted for rotation about a rotational axis, and the recess is preferably asymmetrical with respect to the rotational axis. In another embodiment, the recess includes an inner contour, the wobble shaft includes an end facing the clutch driver and having an outer contour, and the outer contour of the end substantially matches the inner contour of the recess.
In accordance with another aspect of the present invention, the clutch includes a clutch driver rotatably positioned within the housing adjacent the wobble shaft, a first clutch disk connected with the gear and positioned between the gear and the clutch driver, and a second clutch disk connected with the clutch driver and positioned between the gear and the first clutch disk. Preferably, the clutch driver includes a hub portion, and the first and second clutch disks are mounted about the hub portion. The gear can also be mounted about the hub portion.
In one embodiment, the gear includes a plurality of grooves, and the first disk includes a plurality of splines positioned within the grooves. The clutch driver can also include a plurality of grooves, and the second clutch disk can include a plurality of splines positioned within the grooves. Preferably, the gear includes a recess, and the first and second clutch disks are positioned within the recess.
In accordance with another aspect of the present invention, the clutch includes a clutch driver rotatably positioned within the housing adjacent the wobble shaft, the clutch driver including a relief ledge for providing clearance between the clutch driver and the wobble plate.